azidopine and Leukemia--Myelogenous--Chronic--BCR-ABL-Positive

P-glycoprotein plays a key role in multidrug resistance of tumor cells. In order to elucidate the possible quarternary structure/function relationship of P-glycoprotein, we treated multidrug-resistant human leukemia K562/ADM cells with the crosslinking reagent, disuccinimidyl suberate. In addition to 180K P-glycoprotein, a 340K protein was immunoprecipitated with an anti-P-glycoprotein monoclonal antibody, MRK-16. The 340K protein is most probably a dimeric P-glycoprotein, since only the 180K P-glycoprotein was immunoprecipitated with MRK-16 when K562/ADM cells were treated with the cleavable crosslinking reagent, dithiobis(succinimidylpropionate), and analysed under reduced conditions. The dimeric P-glycoprotein was photolabeled with [3H]azidopine like the 180K monomeric P-glycoprotein and the photolabeling was inhibited by excess amount of vincristine and verapamil. The dimeric P-glycoprotein could be a functionally active form of the protein involved in the transport of antitumor agents.

Topics: Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; ATP Binding Cassette Transporter, Subfamily B, Member 1; Azides; Dihydropyridines; Doxorubicin; Drug Resistance; Humans; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Macromolecular Substances; Membrane Glycoproteins; Mitolactol; Mitomycins; Precipitin Tests; Succinimides; Tumor Cells, Cultured; Verapamil; Vincristine

We have examined the expression of P-glycoprotein (P-gp) in adult T-cell leukemia (ATL) samples from 25 patients. Based on immunoblotting with a monoclonal antibody against P-gp, C219, 8 of 20 ATL patients were P-gp positive at the initial presentation. All 6 patients at the relapsed stage were P-gp positive, and refractory to chemotherapy. The expression of MDR1 mRNA in P-gp-positive ATL cells was increased at the relapsed stage of one patient. P-gp of this patient was photolabeled with [3H]azidopine and the labeling was inhibited with nimodipine, vinblastine and progesterone. These results suggest that P-gp expressed in ATL cells from patients at relapsed stage has the same binding site(s) for the drugs as that in multidrug resistant cells, and is correlated with the refractory nature of the cells to chemotherapy.

Topics: Antibodies, Monoclonal; ATP Binding Cassette Transporter, Subfamily B, Member 1; Azides; Blast Crisis; Cell Line; Dihydropyridines; Gene Expression Regulation, Leukemic; Humans; Immunoblotting; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Leukemia, Myeloid, Acute; Leukemia, T-Cell; Lymph Nodes; Membrane Glycoproteins; Nimodipine; Polymerase Chain Reaction; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Progesterone; RNA, Messenger; Tritium; Vinblastine